title: Contrasting modes of inorganic carbon acquisition amongst Symbiodinium (Dinophyceae) phylotypes.
abstract: Growing concerns over ocean acidification have highlighted the need to critically understand inorganic carbon acquisition and utilization in marine microalgae. Here, we contrast these characteristics for the first time between two genetically distinct dinoflagellate species of the genus Symbiodinium (phylotypes A13 and A20) that live in symbiosis with reef-forming corals. Both phylotypes were grown in continuous cultures under identical environmental conditions. Rubisco was measured using quantitative Western blots, and radioisotopic (14) C uptake was used to characterize light- and total carbon dioxide (TCO2 )-dependent carbon fixation, as well as inorganic carbon species preference and external carbonic anhydrase activity. A13 and A20 exhibited similar rates of carbon fixation despite cellular concentrations of Rubisco being approximately four-fold greater in A13. The uptake of CO2 over HCO3 - was found to support the majority of carbon fixation in both phylotypes. However, A20 was also able to indirectly utilize HCO3 - by first converting it to CO2 via external carbonic anhydrase. These results show that adaptive differences in inorganic carbon acquisition have evolved within the Symbiodinium genus, which thus carries fundamental implications as to how this functionally key genus will respond to ocean acidification, but could also represent a key trait factor that influences their productivity when in hospite of their coral hosts.
authors.affiliation: Coral Reef Research Unit, Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK.
authors.forename: Patrick
authors.initials: P
authors.lastname: Brading
authors.affiliation: College of Earth, Ocean, and Environment, University of Delaware, 700 Pilottown Rd, Lewes, DE 19958, USA.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Warner
authors.affiliation: Coral Reef Research Unit, Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Smith
authors.affiliation: Coral Reef Research Unit, Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Suggett
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D037421:Anthozoa / Q000469:parasitology*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D004141:Dinoflagellida / Q000254:growth & development / Q000378:metabolism* / Q000502:physiology / Q000528:radiation effects; D004579:Electron Transport; D008027:Light; D058086:Microalgae / Q000254:growth & development / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects; D010788:Photosynthesis; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D013045:Species Specificity; D013559:Symbiosis
chemical_list: D002734:Chlorophyll; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase; D000077194:Chlorophyll A
keywords: Symbiodinium; carbon acquisition; carbon-concentrating mechanism (CCM); dinoflagellate; microalgae; ocean acidification